increasing max_pred_locks_per_transaction, what shuold I look for?

Hi all,

I've got a situation where I need to increase max_pred_locks_per_transaction value to allow the addition of a slony node to complete on postgres 9.1. We had this issue before and we increased the default value from 64 to 128, but now we have a sync that takes even longer and the value for 128 isn't enough either.

Looking at the activity I saw in pg_locks, I believe I need to set it to at least 256, but a value this high I want to make sure that I don't cause other issues with the system. The docs mention that it may need to request more system v shared memory, but should I also re-calculate other parameters such as work_mem, shared_buffers, etc?

Current System:
Postgres 9.1.3
252 GB system memory
shared_buffers 40GB
work_mem 200MB
max_connections = 300
max_prepared_transactions = 0

free -g
total used free shared buffers cached
Mem: 252 239 12 0 1 221

I have a lot of cashed memory, but I just want to make sure this isn't something that cascades out of control and I'm suddenly having major 'out of memory' issues.

thanks in advance,
- Brian F